There are numerous examples known from the patent literature of the production of electrocoat materials. Compounds of tin and/or of bismuth, in particular, are employed as crosslinking catalysts in these materials. In recent times, the bismuth compounds have been used preferentially as crosslinking catalysts, since in addition to their high activity they also possess a low toxicity as compared with the tin compounds. The use of bismuth compounds as catalysts in the formation of urethane structures from isocyanate groups and hydroxyl groups is already well established (J. H. Saunders and K. C. Frisch, Polyurethanes, Chemistry and Technology from High Polymers, Vol. XVI, Part 1, Interscience Publishers, a division of John Wiley and Sons, New York, 4th Printing, July 1967, page 167). To date, however, the use of bismuth compounds as catalysts in connection with the production of electrocoat materials has been very limited. In EP 0 642 558 the bismuth compounds that are candidates for the use of electrocoat materials are significantly restricted, since the readily available salts with relatively long-chain acids, such as bismuth octanoate and bismuth neodecanoate, for example, cause disruptions as a result of oily exudations when used in cationic binders. Furthermore, as a result of being mixed into the binder or into a pigment paste, inorganic bismuth compounds are said to be difficult to disperse and in this form to have only a low catalytic activity. European patent EP 0 739 389 describes a simplified process for producing a corrosion control coating by means of electrodeposition coating, where the electrodeposition coating material comprises bismuth lactate or bismuth dimethylpropionate. Further possible bismuth compounds are mentioned, but without any details; in particular, the examples use only the salts of lactic acid and dimethylpropionic acid. Bismuth subnitrate is not mentioned. Further bismuth complexes based on amino acids (EP 0 927 232) or alkanesulfonic acids (EP 1 163 302) are described as being useful and stable catalyst systems in electrocoat materials. For improving the corrosion control of electrocoat materials DE 100 01 222 A1 cites the use of colloidal bismuth. That German patent uses bismuth salts of aliphatic carboxylic acids. A further use of bismuth salts of organic carboxylic acids is described in an electrocoat material in German patent application DE 44 34 593 A1. Toxic constituents are to be largely avoided in the preparation of that corrosion control coating material. German patent application DE 102 36 350 A1 describes electrocoat materials which comprise bismuth subsalicylate and which flow well, are free from surface defects, and ensure effective corrosion control. These known electrocoat materials, however, require a relatively high baking temperature in order to achieve sufficient crosslinking.
It is an object of the present invention to find new electrocoat materials comprising bismuth compounds, the crosslinking reactions taking place in the electrocoat material of the invention at baking temperatures which are as low as possible.